Unpublished Canadian data on seasonal flu shots and H1N1 stir concern

Sep 24, 2009 (CIDRAP News) – Canadian researchers reportedly have found as-yet-unpublished evidence that people who had a seasonal flu shot last year incurred a higher risk of H1N1 infection, but US and World Health Organization (WHO) officials say they are not aware of any similar findings elsewhere.

The Canadian Press (CP) reported that a series of studies in British Columbia, Quebec, and Ontario seem to suggest that people who received a seasonal flu shot last year were about twice as likely to contract the pandemic H1N1 virus. The findings are spurring an effort by some Canadian public health officials to delay, reduce, or cancel seasonal flu vaccination campaigns this fall.

Details of the findings and the methods that led to them have not been released, as the authors have submitted a paper to a journal and therefore are barred from discussing them, according to the story. But many people in public health in Canada have heard about the data.

The lead authors are Dr. Danuta Skowronski of the British Columbia Centre for Disease Control and Dr. Gaston de Serres of Laval University in Quebec, the story said.

In response to a question at a WHO news briefing today, Dr. Marie-Paule Kieny, director of the agency's Initiative for Vaccine Research, said the WHO is looking into the reported findings. The WHO is trying to assemble a group of experts to review the Canadian data, she said.

So far, "Investigators in other countries have looked at their own data and whether they could find similar observations, and none of the other countries have been able to find anything like that," Kieny added. She said the findings could be real or could be the result of a study bias or other methodologic problems.

She also said many years of experience with seasonal flu immunizations have yielded no other evidence that they cause this type of problem, but the report warrants investigation.

The US Centers for Disease Control and Prevention (CDC) said it was not aware of any similar observations in this country. "This is unpublished data and most importantly nothing that our scientists have seen in the United States," CDC spokesman Tom Skinner told CIDRAP News. "We believe it is advantageous for seasonal and 2009 H1N1 vaccines to be taken as soon as available."

According to the CP story, several infectious disease experts said that British and Australian researchers have not seen the phenomenon observed by the Canadian authors, either. One of the experts called the lack of confirmation elsewhere a "red flag."

Skowronski, the co-author, acknowledged that her paper needs the scrutiny of the peer-review process to uncover any methodologic problems, the CP reported. "We need to be assured that every stone was turned over to make sure what we're reporting is valid," she was quoted as saying.